From German Patent Application 1,964,469 an atomic absorption spectrometer is known wherein the radiation originates from a single light source designed as a line emitter, the radiation of which passing through the sample is frequency modulated by use of the longitudinal Zeeman effect. In this prior atomic absorption spectrometer a hollow cathode lamp is arranged between the pole pieces of a solenoid. One of the pole pieces has a bore through which the measuring light beam passes. Then the measuring light beam is directed through a flame serving as atomizing device and a monochromator and impinges upon a photo-electrical detector. The solenoid is arranged to be switched on and off, whereby the atomic absorption of the sample atoms compensated with respect to the background absorption can be determined from the difference of the signals with the solenoid switched off and switched on. The windings of the solenoid are provided on the pole pieces.
In this prior art atomic absorption spectrometer the emission lines of the line emitting light source are periodically shifted by the Zeeman effect and thus the emitted light frequency is modulated and not the absorption lines of the sample. This may cause problems when a hollow cathode lamp is used as light source because the discharge of the hollow cathode lamp is influenced by the magnetic field, as already mentioned in German Patent Application 1,964,469.
From German Patent Application 2,165,106 it is known to apply the magnetic field of a solenoid arranged to be switched on and off to the atomizing device, i.e. to the sample which is to be atomized, instead to the light source. Therein the atomizing device is a flame. The magnetic field is applied perpendicular to the direction of propagation of the measuring light beam. A splitting of the absorption lines due to the "transverse" Zeeman effect is effected, which again effects a relative shift of the emission lines of the measuring light beam and the absorption lines of the sample. Again it can be discriminated between atomic absorption by the atoms of the element looked for and non-specific background absorption by switching the magnetic field on and off.
When the transverse Zeeman effect is used a spectral line is split into a central line the wave length of which corresponds to the non-shifted wave length of the respective line with the magnetic field switched off and two side lines which relative thereto are shifted to longer and shorter wave lengths. The central line and the side lines are polarized differently. Therefore the influence of the central line can be eliminated by a polarizer. Such a polarizer however causes a light loss of 50%.
Furnaces are known as atomizing devices for the electrothermal atomization of the sample. Graphite tubes serve for this purpose for example, which are held between annular contacts and through which the measuring light beam passes in longitudinal direction. A strong electrical current is passed through the annular contacts through the graphite tube. Thereby the sample introduced into the graphite tube is atomized and forms a "cloud of atoms" within the graphite tube. In this cloud of atoms the element looked for is present in atomic state. Such atomizing devices operating with a graphite tube are known from German Patent Application 23,14,207 and German Patent Application 21,48,783, for example.
It is also known to effect compensation of the background absorption by the Zeeman effect in such atomizing devices which operate with a graphite tube flown through by current in longitudinal direction. For this purpose a alternating magnetic field directed transverse to the direction of propagation of the measuring light beam is applied to the graphite tube by a solenoid. Thereby the transverse Zeeman effect is caused as well, whereby a polarizer in the path of rays is required.
Furnaces for the electrothermal atomization of a sample in an atomic absorption spectrometer are known in which the current is not passed through a graphite tube in longitudinal direction but in circumferential direction. Examples for this are U.S. Pat. No. 4,407,582 and German patent application 35,34,417 as well as the publication in "Analytical Chemistry" 58 (1986), 1973 having substantially the same contents.
A contact arrangement provided with two contacts for the current supply to a transversely heated tubular furance for the electrothermal atomization in atomic absorption spectroscopy is known from not pre-published German patent application P 37,26,533.4 in which contact arrangement the furnace has longitudinal diametrically opposite contact ribs. The contacts of this contact arrangement the axes of which extend perpendicular to the axis of the furnace and to the direction of propagation of the measuring light beam, form a cavity under operational conditions in which the tubular furnace is accomodated. There the furnace is held between v-shaped grooves of the contacts. The cavity is formed substantially by an impression in one of the contacts which is closed by the other contact except for a partion gap. Inert gas passages open into the grooves.
A tubular furnace for the electrothermal atomization of samples in atomic absorption spectroscopy is known from not pre-published German patent application P 37,35,013.7. This furnace comprises a tubular furnace body with contact sockets arranged on opposite sides. The contact sockets have contact ribs extending longitudinally to the tubular proper furnace body adjacent to which are cylindrical contact pieces with conical contact surfaces. These contact ribs have contractions. According to German patent application P 37,35,013.7 these contractions are formed by cylindrical turned out portions. An equal temperature along the furnace body shall be achieved by this design. The contact arangement is similar to that in German patent application P 37,26,533.4 mentioned heretofore.